The invention concerns a rechargeable battery pack, in particular for use in electrical hand-tool devices, comprising a first and a second charging connection and a third control connection, all three being connectable to a charging device to produce a charging connection, and comprising a calculating means responsive to an interface circuit, wherein the interface circuit utilizes the third control connection.
Conventional analog rechargeable battery packs have a temperature probe in the form of an NTC resistor. The NTC resistor is responsive to the charging device via a third control connection of the rechargeable battery pack. In this fashion, heating of the rechargeable battery pack during the charging process can be detected, and the charging current limited or the charging process terminated. Nickel cadmium cells or nickel metal hydride cells are e.g. used for the rechargeable battery packs.
In a further development of this prior art, digital rechargeable battery packs have been provided with a calculating means which is responsive via an interface circuit, with the third control connection of the rechargeable battery pack also being used in this case. A bidirectional communication is thereby established between the charging device and the rechargeable battery pack such that rechargeable battery pack parameters can be transferred to a charging device provided with corresponding intelligence in order to adjust the charging process exactly to the specific rechargeable battery type and its operating parameters. A calculating means as mentioned above denotes any microcontroller or ASIC (application specific integrated circuit) or any other, in particular, programmable calculating device, known per se, for providing a preferably bidirectional communication in order to retrieve information and transfer it to the charging device. In particular, the calculating means may itself be designed and suited to interact with the charging process, i.e. for control in the broadest-sense.
Commercial operation of these rechargeable battery packs is associated with considerable load on all components due to constant use as well as other influences such as mechanical or-temperature-related: effects- any one of which could cause the service life of the rechargeable battery pack, i.e. the maximum operating-time, to-be exhausted or cause data transfer, i.e. the intended transfer of information in order to identify the specific rechargeable battery type, to be temporarily or permanently impaired. Temporary impairment could e.g. occur when a computer fails to respond for no obvious reason and could be corrected by re-booting. In such a situation an “intelligent” charging device may fail to receive proper information for evaluation when the calculating means of the rechargeable battery pack is active and, in consequence thereof, the charging device could e.g. assume that a conventional analog rechargeable battery pack had been inserted into the charging recepticle of the charging device and a corresponding charging routine might be executed. This would have destructive consequences if a digital rechargeable battery pack, without overheating protection in the form of an NTC resistor as is common in analog rechargeable battery packs, were actually being charged. In this case, the rechargeable battery pack would certainly be destroyed in such a charging process, which entails 15 to 60 minutes at charging currents of between 1 and 5 amperes. The use of Lithium ion rechargeable cells thereby represents e.g. considerable danger to the user and also to the environment. This also applies, in principle, to rechargeable battery packs having nickel cadmium cells or nickel metal hydride cells.
It is the underlying purpose of the present invention to effectively address the above-mentioned problem by providing digital rechargeable battery packs comprising the conventional two charging connections as well as the third control connections in conventional analog rechargeable battery packs, such that both packs can be charged using the same charging devices, while reliably preventing a digital rechargeable battery pack, without simple temperature sensor, e.g. on the basis of an NTC resistor, from being erroneously identified as a conventional analog rechargeable battery pack, to therefore prevent destruction of the rechargeable battery pack due to an erroneously selected charging process.